In this project I take an Arduino Mini Pro connect it to a custom made Etch A Sketch panel and use it to control a Blacknose laser cutter. The result is hours of crazy laser cutting fun, which we will be taking round most of the UK Maker Faires this year for JustAddSharks.co.uk

he Etch A Sketch has 2 knobs in the lower corners, one controls movement in the X axis and the other controls movement in the Y Axis. The laser cutter also has an X and a Y axis so each knob is mapped directly to the appropriate axis. The laser is only turned on while the axis are moving which prevents the laser from setting fire to the material it is cutting.

The control is all done using the Arduino Mini Pro which shows that small can also be powerful. The lack of processing speed to produce stepper motor pulses is compensated for using the hardware PWM modules in exactly the same ways as described in my previous instructable.

We will be taking this whole project to the UK Maker Faire at the end of April as well as numerous other UK Maker Faires this year so if you're lucky you can come and visit us and give it a try for yourself.

Step 1: Quadrature Inputs

The rotary encoders used in this project produce quadrature output wave signal. 
Quadrature output is sent over two data lines, each line carries a square wave signal but the two lines are 90 degrees out of phase.

By counting the number of pulses on either square wave it is possible to determine how far the encoder has been turned. It is important to know the direction that the knob is turning to decide if the step should be added or taken away from the total count. This is where the second data line can be used.

If you check the state of the 'B' data line as the state of the 'A' line changes you can determine which direction the knob was turning. In the example images I have highlighted the falling edge of the 'A' signal. While the knob is being turned clockwise the 'B' line is high as the 'A' line falls. When the knob is turned anticlockwise the 'B' line is low.

For ultra fast detection of the quadrature input the first data line could easily be connected to an interrupt input and set to detect the signal edge. Each time the interrupt triggers the count can be changed and by checking the second line on a standard input you know to add or subtract from the count.

<p>Well done! Clear directions and a novel interface.</p><p>Have you had a chance to use it with students? I think the etch-a-sketch is an awesome way to teach the cartesian grid and has so many learning applications in technology. (Like the the Makelangelo </p><p><a href="http://www.marginallyclever.com/shop/drawing-robots/makelangelo-3-complete-kit" rel="nofollow">http://www.marginallyclever.com/shop/drawing-robots/makelangelo-3-complete-kit</a></p><p>) I'm hoping someone can post a few student made pictures in the future.</p>
My thought process on this was... <br>Cool, but I'm rubbish with Etch-a-sketch... <br>Oh it'll be a Maker Faire UK, I'll login and comment that I'll see you there... <br>Bloody hell, haha it's Martin. <br>Very much looking forward to the Faire, as Hitchin Hackspace will be exhibiting there (our first one). I'll let you have a go on what we're taking. Trust me, you'll love it.
<p>My first reaction to it was, WUT?</p>
<p>I agree this is fascinating but I suck at etch a sketch. So basically you have taken a precise utlra fine laser cutting machine and let an idiot like me screw up some nice wood and make square boobs on it. :)</p>
<p>Fascinating. So you're controlling the lasercutter with the knobs on the Etch-A-Sketch?</p>

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